This invention relates to sealing of a variable volume device formed of rectlinear pistons and casing, the sealing utilizing rollers and sealing strips to separate force transfer and sealing functions.
Variable volume devices utilizable as pneumatic or fluid motors, compressors, internal or external combustion engines, etc. are known in many variations and configurations. Particularly in positive displacement embodiments, the use of a reciprocating piston fitted in a cylinder and sealed by means of rings extending circumferentially around the piston is well known in the art. Other arrangements having apparent advantages in the mechanical configuration thereof, such as the Wankel rotary engine, have been found to suffer at least initially critical draw backs in the sealing between the static and moving components. Simplicity of the cylindrical piston ring in many respects offset the additional volume, production expense, weight, etc. of the ubiquitous piston and cylinder arrangement.
One previously proposed particularly advantageous design for a variable volume apparatus, apparently a century old Root's design, utilizes a rectilinear casing containing a pair of rectilinear pistons therein. An outer piston is reciprocated within the casing to define variable volumes at either end thereof. The inner piston reciprocates relative to the outer piston in a direction transverse to the direction of reciprocation of the outer piston in a relative sense, and rotates in an absolute sense, to provide third and fourth variable volumes between the inner and outer pistons. Examples of such structures are to be found in U.S. Pat. No. 2,013,862 and British Patent No. 479,705, issued to Skarlund. The advantages of light weight relative to displacement, compactness, simplicity of parts, etc. of such a design are readily apparent. However, despite these advantages, no widely accepted utilization of such design has resulted. As with other designs utilizing linear or flat surfaces bearing upon flat surfaces, it would appear that the lack of practical application is attributable to the difficulty of sealing such devices. Also, in contrast to the situation with a reciprocating cylindrical piston in which the greatest forces are transverse to the direction of sealing, the rectangular piston arrangement particularly involves substantial forces at the sealing area between the inner and outer pistons thus substantially complicating the task of providing effective and efficient sealing therebetween.